Over the course of April the upsurge of violence in Iraq has killed close to
100 US troops - the worst monthly casualty figures since the invasion of Iraq began.

What began as an irritant in the aftermath of war has now turned into a complex insurgency presenting a whole series of problems to US commanders.

The dramatic rise in US combat deaths is a measure of the twin-pronged offensive from former regime loyalists and elements of the Shia community.

Ambushes and urban fighting are causing the most US casualties and we still have no real understanding of the extent of damage to civilian lives and property, which could be considerable.

Spain's withdrawal is more a political than a military blow to the US

The attacks against key US supply routes are especially damaging.

They cause a steady trickle of casualties, interrupt US logistics and dissuade Iraqi civilian freight and trucking firms from cooperating with the Americans.

The closure of some sections of major roads to all but military traffic only adds to the general sense of insecurity.

With US spokesmen admitting that newly-recruited Iraqi forces are not up to the job, some 20,000 US troops have had their tours of duty in Iraq extended - and more units could be on their way if needed.

While US spokesmen were warning that their patience was running out in Falluja, US commanders do appear have agreed with local leaders to try to find some negotiated settlement to the stand-off.

There has been some criticism of what has been described as "the excessive use of force" by US marines ringing the city - though they have come under heavy fire and suffered casualties themselves.

The coalition authority clearly though wants to end this curent crisis without further violence if at all possible.

This current upsurge of violence is containable.

But what it says about the future is most worrying.

Mistakes

All the talk of interim Iraqi governments and the hand-over of power cannot obscure one fundamental fact; the Americans are no closer to establishing a viable governing formula for Iraq that takes account of the very different interests of the majority Shia, the Sunnis and the Kurds.

Worse still, the inability of the US to provide stability in Iraq after a year of occupation has prevented the emergence of a calmer climate in which such issues might have been debated.

It will be up to the Americans - at least for now - to come up with more men

Ordinary Iraqis perceive that things are getting worse, whatever the optimistic press briefings from the coalition authority in Baghdad.

And this too makes the task of the US military on the ground even harder.

Critics say that to some extent the US is the author of its own misfortunes.

Many more troops were needed at the outset of the occupation to avoid a security vacuum into which the forces of disorder would move.

The disbanding of the Iraqi army too was a huge mistake.

Even the Americans now admit that their hastily recruited and trained Iraqi security forces are not up to the job.

Spain's withdrawal of its 1,300 troops may provide some short-term problems on the ground but its impact is more political than practical.

It signals a very public vote of no-confidence in the occupation and, while other troop-contributing countries may take a more robust view, the repercussions of Spain's decision will influence the public debate in many countries.

Election year

In fairness the Americans never expected it to be like this, though it is not clear if this was just naivety, misjudgement, wishful thinking, or a combination of all three.

It is hard to say exactly how many troops were needed in post-war Iraq.

Comparisons with the Balkans and other peace-keeping missions are not necessarily helpful, though many experts believe that the US did require many more boots on the ground than were available.

MAIN FOREIGN TROOPS IN IRAQ

US: 135,000

UK: 8,700

Italy: 3,000

Poland: 2,400

Ukraine: 1,650

Spain: 1,300

Australia: 850

Japan: 550

The Pentagon first hoped to draw in large numbers of allied troops. There is a reasonably impressive list of troop-contributing countries but most of their contributions are small.

Key players with the sort of combat-ready troops the US needs - like France and Germany - have sat things out on the sidelines.

The next Pentagon option was to increasingly turn things over to newly-recruited Iraqi forces. But this plan too has foundered for the immediate future.

It will be up to the Americans - at least for now - to come up with more men. But extending tours in Iraq is hugely unpopular among service families.

It was hoped that US troop levels would be coming down by now - this is after all an election year - and it is an issue on which Mr Bush could become very vulnerable.